u6 SCIENCE PROGRESS 



benzene). They are therefore considered as reduced cymene 

 derivatives, and di-, tetra- and hexa-hydrocymenes are known. 

 By the linking up of two or more reduced benzene rings the 

 more complicated terpenes are built up (sesquiterpenes, poly- 

 terpenes). Some of the poly-terpenes show the same colour 

 reaction as cholesterin. 



Recent researches have made it very probable that in 

 cholesterin five reduced rings are linked together, and the 

 following formula has been tentatively put forward as explaining 

 satisfactorily our present knowledge of the substance : 



CH 3 



\ / CH 3 



Functions of Lipoids. — With regard to the biological position 

 of the lipoids we can infer from their general occurrence that 

 they are of fundamental importance for the living organism, and 

 there seems to be a good deal of truth in the opinion of Bang, 

 that the importance of proteins as carriers of life (" Trager des 

 Lebens ") has been over-estimated, whilst that of the lipoids has 

 been neglected. The phosphatides, from their composition, may 

 act as intermediary agents between different groups of com- 

 pounds. We easily recognise a relationship to fats, from which 

 perhaps they are formed, the fats contributing two of the 

 constituents of lecithin, the fatty acid and glycerin. During 

 the process of digestion lecithins also behave like fats. They 

 are hydrolysed by the action of lipase, the fat-splitting enzyme 

 of the pancreas (Meyer). The question has, however, not yet 

 been decided if the hydrolysis in the intestinal canal is a com- 

 plete one, or if unchanged lecithin is absorbed as such. It is, 

 however, probable that complete cleavage does take place. 

 It is pretty certain that all ferments manifest a reversible action ; 

 this has certainly been proved in the case of lipase ; moreover, 

 lipase appears to be widely distributed in the tissues, and so it may 

 be assumed that a synthesis of lecithins from their cleavage 

 products takes place in the body. The general occurrence of 

 another cleavage product of lecithin, namely choline, in nearly 

 all organs where cell activity is marked, may be related to this 

 question (Rosenheim). From another point of view the phos- 

 phatides may form a link with the cell nucleins, which possibly 

 obtain their necessary supply of phosphorus from this source. 



